In the quadratic equation ax2 plus bx plus c 0 if b2 - 4ac?

If you mean b^2 -4ac then it is the discriminant of a quadratic equation.

If the discriminant equals 0 then the equation has 2 equal roots.

If the discriminant is greater than 0 then the equation has 2 different roots.

If the discriminant is less than 0 then it has no real roots.